The use of images that are successively captured from a satellite to detect variations of a line of sight of images is known, and that this line of sight can be corrected to compensate for the variations.
Whenever the line of sight is fixed with respect to the satellite, modifications of the orientation of the entire satellite that are performed to compensate for variations in the line of sight can be used to stabilize the satellite's attitude, that is, it's angular orientation with respect to external markers. In particular, those markers can be imaged in the captured images.
Another application of the stabilization of the line of sight of an imaging system on-board a satellite consists in reducing blur in captured images. This blur is caused by unwanted variations of the line of sight, which occur during exposure of the photodetectors of the image sensor. These unwanted variations may be caused by vibrations produced by moving elements of the satellite, such as attitude control actuators, or a filter wheel, or even fuel in the liquid phase.
In general, the efficiency of stabilization of the line of sight of the imaging system increases when the latency is shorter between the occurrence of a new variation in the line of sight and the moment when the result of the characterization of this variation is obtained. When this latency is short, it is possible to efficiently command the satellite's attitude control system, or a mobile imaging system support, or a variable pointing system, so as to compensate, at least in part, for the variation in the line of sight that has been detected and characterized. In other words, it is then possible to efficiently stabilize the line of sight and provide high responsiveness with respect to its unwanted variations.
Another general object of the methods of line-of-sight stabilization consists in producing successive characterizations of the direction of this line of sight based on a sufficiently high frequency of characterization.
Still another object of the line-of-sight stabilization methods for an imaging system on-board a satellite consists in enabling such stabilization with a high degree of precision. In particular, it is necessary to characterize the variations in the line of sight with a precision greater than that which can be obtained using gyroscopes or star sensors.
Lastly, another object of the invention consists in obtaining improved line-of-sight stabilization that does not require that additional heavy, cumbersome, or costly equipment be placed on-board the satellite. In other words, the invention seeks to improve stabilization of the line of sight by modifying the equipment that is already present on-board the satellite as little as possible.